In a serial bus system, message processing based on a stored communication of messages is a standard procedure. The messages are communicated from bus node to bus node, wherein the messages of the currently-processing bus node are treated preferentially. With this type of node-related communication of messages, a real-time capability cannot be provided, because the dwell time of a message in the memory of the bus nodes is unpredictable and can, at the very most, be indicated statistically.
By contrast with synchronous buses, in which a certain portion of a synchronous channel is assigned to a special node for a certain time, an asynchronous control allows the communication of several requests for small data quantities, without the need for an interruption of the message transmission. Documents U.S. Pat. No. 5,719,858 and EP 1 465 370 A1 propose systems, which allow an asynchronous transmission on the basis of a synchronous physical channel. Accordingly, it is possible to provide an environment for communication between two nodes, which also satisfies stringent requirements with regard to time conditions. For example, in the case of U.S. Pat. No. 5,719,858, several nodes are connected to a TDM (time division multiplexed) bus, on which a certain bandwidth is made available to several bus nodes. This is then distributed to the individual units using a time-slice method. In the case of EP 1 465 370 A1, a data telegram is subdivided for asynchronous processing and packed into so-called “clocked frames”, so that it is possible to allow a synchronous data transmission on a synchronous bus.
The Manchester coding method has been established as the standard method for bus systems. It is simple to implement, direct-current-free and allows the auto-synchronization of stations communicating with one another, so that a separate clock-pulse supply is not required.